Human intestinal diseases are comprised of a wide variety of pathological states, including chronic illnesses such as inflammatory bowel disease (IBD) and intestinal failure, and thus represent a significant public health burden. A major challenge for intestinal research therefore is to develop a more detailed understanding of intestinal biology that will lead to new interventions to prevent and treat these debilitating intestinal diseases. The long-term goals of my research are to understand the molecular mechanisms that regulate intestinal stem cells (ISCs), and how these pathways can be utilized for regenerative medicine or modulated to improve clinical outcomes and quality of life of patients suffering these chronic illnesses. The objective of this grant is to determine the role of ADAM10, which is an a-secretase (i.e., ectodomain sheddase) that is predicted to regulate key extracellular signaling events, including Notch signaling in ISCs and their progeny within the stem cell niche. Our central hypothesis is that ADAM10 acts at multiple levels in adult crypts to maintain ISCs and to control progenitor proliferation and lineage specification, and that these same signals play a critical role during intestinal injury and regeneration. Our hypothesis has been formulated on the basis of our own preliminary data us- ing intestine-specific ADAM10-deficient mice. The rationale for the proposed research is that, by understanding the role for ADAM10 signaling in maintaining ISCs/progenitor populations during normal intestinal homeostasis, and in models of injury/regeneration, we will define ADAM10 as a new molecular target, resulting in innovative approaches for stem cell therapies in regenerative medicine and for treatment of intestinal diseases. In Aim 1, we will define the requirements for ADAM10 in distinct ISC populations through cell lineage tracing. In Aim 2, we will determine the requirements for ADAM10 in distinct ISC population in intestinal inju- ry/regeneration. In Aim 3, we will determine the role of ADAM10 in progenitor proliferation and cell lineage specification using conditional ADAM10-deficient mice. At the conclusion of these studies, we will have expanded our knowledge on the importance of ADAM10 signaling in ISC populations during intestinal homeosta- sis under normal and regenerative conditions, evaluated its contribution to the regulation of progenitor cell proliferation and cell fate decisions, and determined the significance of ADAM10-mediated Notch signaling in these events.